import sys
import numpy as np

def fwadd(data, p, x):
    n = data.shape[0]
    p += 1
    while p <= n:
        data[p-1] += x
        p += p & -p

def fwsum(data, l, r):
    s = 0
    while r > 0:
        s += data[r-1]
        r -= r & -r
    while l > 0:
        s -= data[l-1]
        l -= l & -l
    return s



def main():
    n = int(input())
    S = np.fromstring(input(), np.int64, sep=' ') - 1
    fw = np.zeros(n, np.int64)
    a = 0
    for s in S:
        a += fwsum(fw, s, n)
        fwadd(fw, s, 1)
    print(-1 if a & 1 else 1)







if __name__ == '__main__':
    main()